Study Of Broadband Plasmonics Metamaterial Electromagnetic Absorber In Mid-infrared Frequencies

Plasmonic metamaterials are artificial electromagnetic materials with subwavelength-scale metallic and dielectric nanostructures, which possess exotic electromagnetic properties that are unattainable in nature. Plasmonics metamaterials have attracted great interest and been extensively studied among scientific research community in last decade. Among various applications of plasmonic metamaterials, one important aspect is plasmonic metamaterial absorbers(PMAs). While early absorbers based on high material absorption are inevitably bulky, the geometric structure is found as a crucial factor. The perfect light absorption in PMAs is based on the excitation of surface plasmon polaritons(SPPs) in nanostructures. Such PMAs generally own properties like deep subwavelength thickness, perfect absorption, and easy tunable resonant frequency, and they have been demonstrated as promising candidates for applications in emitters, sensors, solar cells, and subwavelength imaging both theoretically and experimentally. This dissertation focuses on the research and design of broadband mid-infrared plasmonic metamaterial absorbers and the main content can be summarized as follows:(1) We have proposed and investigated a mid-infrared grating-like metamaterial absorber for multiband light absorption. This absorber has ultra-compact structure and can absorb mid-infrared light with longer wavelength by small unit. Besides, due to the coupling effects between adjacent units, a redshift effect of the spectra is observed theoretically and numerically when the distance between the subunits is reduced. As far as we know, such absorber is the most compact absorber structure in the mid-infrared region. An equivalent LC model is used to analyze and explain the physics mechanism of light absorption. As an example, a four-band absorber with period ?=3.34?m has been designed, the spectra has four absorption peaks, whose resonant wavelengths are 6.9, 7.9,8.9 and 9.97 ?m with absorption rate 99.9%,99.2%,96.1% and 87.4%, respectively.(2) We have presented a broadband plasmonic metamaterial absorber with multi-cavity structure in the infrared region, which can efficiently broaden absorption bandwidth while keeps compact and ultrathin structure feature. In order to avoid the degeneration between two contiguous resonances, which dramatically reduces the bandwidth, we introduce a zigzag design rule to arrange the cavities within a compact unit. Meanwhile, a two-layer and three-layer absorber are designed. The central band wavelength is 8.1 ?m and the FWHM(Full width at half maximum) are 25% and 48%, respectively. It also has an incident-angle-insensitive feature and can be extended to other wavelength band such as terahertz and microwave region.(3) We have designed and numerically investigated a tunable graphene-loaded metamaterial absorber with cross-shaped split gap for broadband light modulation in the mid-infrared region. The light-graphene interaction can be greatly enhanced due to the coupled magnetic resonances, resulting in large tunable wavelength range and deep modulation depth in a wide wavelength range. The numerical results shows that when the Fermi energy EF=0.6 eV, the relative wavelength tuning range of the two resonant peaks are 20.1% and 25.5%, which are far more better than previous works. An effective inductance of graphene model is presented to explain and predict the modulation behavior and the relationship between wavelength tuning range and geometric factor. Our designs may find applications in a variety of areas, including sensing, modulating and biochemical detecting.